U.S. patent number 8,141,646 [Application Number 12/486,121] was granted by the patent office on 2012-03-27 for device and method for gas lock detection in an electrical submersible pump assembly.
This patent grant is currently assigned to Baker Hughes Incorporated. Invention is credited to Robert D. Allen, Dick L. Knox, John Michael Leuthen, Jerald R. Rider, Bryan D. Schulze, Brown L. Wilson, Tom G. Yohanan.
United States Patent |
8,141,646 |
Allen , et al. |
March 27, 2012 |
Device and method for gas lock detection in an electrical
submersible pump assembly
Abstract
A device and method can detect, and also break, an occurrence of
gas lock in an electrical submersible pump assembly in a well bore
based upon surface or downhole data without the need for operator
intervention. To detect an occurrence of gas lock, an instantaneous
value is monitored using a sensor. Then a controller compares the
instantaneous value to a threshold value over a predetermined
duration to thereby detect the occurrence of gas lock in the
electrical submersible pump assembly. Sensors can include, for
example, a differential pressure gauge, a pressure gage located in
a pump stage located toward the inlet, a fluid temperature sensor
located toward the discharge, a free gas detector located near the
pump discharge, an electrical resistivity gage, a flow meter
located within surface production tubing, and a vibration sensor
attached to a tubing string to measure a vibration signature.
Inventors: |
Allen; Robert D. (Claremore,
OK), Leuthen; John Michael (Claremore, OK), Knox; Dick
L. (Claremore, OK), Rider; Jerald R. (Tulsa, OK),
Yohanan; Tom G. (Broken Arrow, OK), Wilson; Brown L.
(Tulsa, OK), Schulze; Bryan D. (Owasso, OK) |
Assignee: |
Baker Hughes Incorporated
(Houston, TX)
|
Family
ID: |
43352954 |
Appl.
No.: |
12/486,121 |
Filed: |
June 17, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090250210 A1 |
Oct 8, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12144092 |
Jun 23, 2008 |
7798215 |
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60946190 |
Jun 26, 2007 |
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Current U.S.
Class: |
166/369; 166/105;
166/250.15 |
Current CPC
Class: |
F04D
9/001 (20130101); F04D 15/0088 (20130101); E21B
43/128 (20130101); F04D 15/0066 (20130101); F04D
15/0209 (20130101); F04D 13/10 (20130101) |
Current International
Class: |
E21B
43/00 (20060101) |
Field of
Search: |
;166/369,105,250.15
;417/443,444,554 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
David L. Divine, Automatic Pump-Off Control for the Variable Speed
Submersible Pump, 55th Annual Fall Technical Conference and
Exhibition of the Society of Petroleum Engineers of AIME, Sep.
21-24, 1980. Society of Petroleum Engineers of AIME, Dallas, Texas.
cited by other .
International Search Report and Written Opinion dated Nov. 20,
2008, 7 pages. cited by other.
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Primary Examiner: Neuder; William P
Attorney, Agent or Firm: Bracewell & Giuliani LLP
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part of co-pending U.S.
patent application Ser. No. 12/144,092, by Leuthen et al., titled
"Device, Method and Program Product to Automatically Detect and
Break Gas Locks in an ESP" filed on Jun. 23, 2008, which claims
priority to U.S. Provisional Patent Application No. 60/946,190, by
Leuthen et al., titled "Device, Method and Program Product to
Automatically Detect and Break Gas Locks in an ESP" filed on Jun.
26, 2007, all of which are each incorporated herein in their
entireties.
Claims
That claimed is:
1. A computer-implemented method of detecting an occurrence of gas
lock in a multi-stage electrical submersible pump assembly for
pumping fluid in a well bore, the well bore extending downward from
a surface, the assembly including a multi-stage electrical
submersible pump having an inlet and a discharge, a pump motor to
drive the pump, and a discharge line for transporting pumped fluid
from the pump discharge to the surface, the method comprising:
monitoring via a sensor an instantaneous value of a property of a
fluid associated with an electrical submersible pump assembly; and
comparing the instantaneous value to a threshold value over a
predetermined duration by a controller configured to receive data
from the sensor and to detect the occurrence of gas lock in the
electrical submersible pump assembly, wherein the sensor includes
one or more of the following: a differential pressure gauge for
measuring a differential pressure of the fluid between the pump
inlet and pump discharge, a pressure gage located in a pump stage
located toward the inlet to measure a pressure, a fluid temperature
sensor located toward the discharge, a free gas detector located in
a pump stage near the pump discharge, an electrical resistivity
gage located within the pump, a flow meter located within surface
production tubing, and a vibration sensor attached to a tubing
string to measure an acceleration of the fluid within the tubing
string to determine a vibration signature responsive to the
measured acceleration of the fluid.
2. A computer-implemented method of claim 1, wherein the sensor
comprises a differential pressure gauge, wherein the step of
monitoring via a sensor comprises measuring a differential pressure
of the fluid in the pump between the pump inlet and pump discharge,
and wherein the step of comparing the instantaneous value to a
threshold value comprises generating the threshold value by the
controller responsive to historical data of values associated with
the sensor.
3. A computer-implemented method of claim 2, wherein the step of
comparing the instantaneous value to a threshold value comprises
generating the threshold value based on a decrease of about 50% of
an average of the instantaneous values from a predetermined range
of the historical data, and wherein the predetermined duration is a
period of about 30 seconds.
4. A computer-implemented method of claim 1, wherein the sensor
comprises a pressure gage, and wherein the step of monitoring
comprises measuring a pressure of the fluid located in a pump stage
located toward the inlet, and wherein the step of comparing the
instantaneous value to a threshold value comprises generating the
threshold value with controller responsive to historical data of
values associated with the sensor.
5. A computer-implemented method of claim 4, wherein the step of
comparing the instantaneous value to a threshold value comprises
generating the threshold value based on a decrease of about 30% of
a peak of the values over a period of about 3 minutes, and wherein
the predetermined duration is a period of about 30 seconds.
6. A computer-implemented method of claim 1, wherein the sensor
comprises a fluid temperature sensor, wherein the step of
monitoring comprises measuring a temperature of the fluid located
in a pump stage located toward the discharge, and wherein the step
of comparing the instantaneous value to a threshold value comprises
generating the threshold value with controller responsive to
historical data of values associated with the sensor.
7. A computer-implemented method of claim 6, wherein the step of
comparing the instantaneous value to a threshold value comprises
generating the threshold value based on an increase of about 20% of
an average of the values over a period of about 5 minutes, and
wherein the predetermined duration is a period of about 30
seconds.
8. A computer-implemented method of claim 1, wherein the sensor
includes a free gas detector located within the pump.
9. A computer-implemented method of claim 8, wherein the threshold
value is a level of free gas of about 50% by volume, and wherein
the predetermined duration is a period of about 30 seconds.
10. A computer-implemented method of claim 1, wherein the sensor
includes an electrical resistivity gage located within the
pump.
11. A computer-implemented method of claim 1, wherein the sensor
includes a flow meter located within surface production tubing.
12. A computer-implemented method of claim 11, wherein the
threshold value is a flow of about zero, and wherein the
predetermined duration is a period of about 30 seconds.
13. A computer-implemented method of claim 1, wherein the sensor
includes a vibration sensor attached to a tubing string to measure
an acceleration of the fluid within the tubing string; wherein
comparing the instantaneous value to a threshold value over a
predetermined duration comprises determining a vibration signature
responsive to the measured acceleration of the fluid; and wherein
the threshold value is one or more predetermined vibration
signatures stored in memory and associated with gas lock.
14. A computer-implemented method of claim 1, further comprising:
breaking the detected occurrence of gas lock by the substeps of:
(a) maintaining a pump operating speed for a first predetermined
period defining a waiting period to facilitate a separation of gas
and liquid located above the pump; (b) reducing the pump operating
speed to a predetermined value defining a flush value for a second
predetermined period defining a flush period so that the fluid
located above the pump falls back through the pump flushing out any
trapped gas; and (c) restoring the pump operating speed to the
previously maintained pump operating speed.
15. A submersible pump assembly, comprising: a multi-stage
electrical submersible pump located in a well bore for pumping a
fluid, the pump having an inlet and a discharge; a pump motor
located in the well bore, to drive the electrical submersible pump;
a discharge line for transporting pumped fluid from the pump
discharge to the surface; a sensor to measure a property of a fluid
associated with the pump, wherein the sensor includes one or more
of the following: a differential pressure gauge for measuring a
differential pressure of the fluid between the pump inlet and pump
discharge, a pressure gage located in a pump stage located toward
the inlet to measure a pressure, a fluid temperature sensor located
toward the discharge, a free gas detector located in a pump stage
near the pump discharge, an electrical resistivity gage located
within the pump, a flow meter located within surface production
tubing, and a vibration sensor attached to a tubing string to
measure an acceleration of the fluid within the tubing string to
determine a vibration signature responsive to the measured
acceleration of the fluid; a controller configured to receive data
from the sensor and to detect an occurrence of gas lock in the
multi-stage electrical submersible pump, the controller comprising:
a processor positioned to detect an occurrence of gas lock, an
input/output interface to communicate with the sensor, and a memory
having stored therein a program product, stored on a tangible
computer memory media, operable on the processor, the program
product comprising a set of instructions that, when executed by the
processor, cause the processor to detect an occurrence of gas lock
by performing the operations of: monitoring an instantaneous value
utilizing the sensor; and comparing the instantaneous value to a
threshold value over a predetermined duration to thereby detect the
occurrence of gas lock in the electrical submersible pump
assembly.
16. A submersible pump assembly of claim 15, wherein the threshold
value is generated by the controller responsive to historical data
of values associated with the sensor.
17. A submersible pump assembly of claim 15, wherein the operations
further include: breaking the detected occurrence of gas lock by
the substeps of: (a) maintaining a pump operating speed for a first
predetermined period defining a waiting period to facilitate a
separation of gas and liquid located above the pump, (b) reducing
the pump operating speed to a predetermined value defining a flush
value for a second predetermined period defining a flush period so
that the fluid located above the pump falls back through the pump
flushing out any trapped gas, and (c) restoring the pump operating
speed to the previously maintained pump operating speed.
18. A submersible pump assembly of claim 15, wherein the
predetermined duration is a period between about 15 seconds and
about 1 minute.
Description
BACKGROUND
1. Field of Invention
The present invention relates, in general, to improving the
production efficiency of subterranean wells and, in particular, to
a device and method which automatically detects gas locks in an
electrical submersible pump assembly ("ESP").
2. Description of the Prior Art
It is well known that gas lock can occur when an ESP ingests
sufficient gas so that the ESP can no longer pump fluid to the
surface due to, for example, large gas bubbles in the well fluid.
Failure to resolve a gas-locked ESP can result in overheating and
premature failure. Conventional practice on an ESP is to set a low
threshold on motor current to determine when the pump is in gas
lock. When this threshold is crossed, the pump is typically stopped
and a restart is not attempted until the fluid column in the
production tubing has dissipated through the pump. This wait time
represents lost production.
It is also known that there are many methods for determining the
proper low current threshold and that an unsatisfactory threshold
can result in either damage to the motor or nuisance shut
downs.
SUMMARY OF INVENTION
In view of the foregoing, embodiments of the present invention
provide a device and method for use with an electrical submersible
pump assembly which can, for example, detect and break an
occurrence of gas lock without the need for operator
intervention.
Embodiments of the present invention can detect an occurrence of
gas lock by monitoring via a sensor an instantaneous value of a
property of a fluid associated with an electrical submersible pump
assembly and comparing the instantaneous value to a threshold value
over a predetermined duration by a controller. The sensor can be
located downhole or at the surface.
In an example embodiment, the sensor can be a differential pressure
gauge for measuring a differential pressure of the fluid in the
pump between the pump inlet and pump discharge, e.g., the bottom
and top of the pump, to determine a drop in pressure. In another
example embodiment, the sensor can be a pressure gage located in a
pump stage located toward the inlet, e.g., the bottom stages of the
pump, to determine a drop in pressure. In yet another example
embodiment, the sensor can be a fluid temperature sensor located
toward the discharge, e.g., the top of the pump, to determine an
increase in temperature.
In other example embodiments, the sensor can be a free gas detector
located within the pump to determine a high level of free gas, or
the sensor can be an electrical resistivity gage located within the
pump to determine a high level of resistivity. Alternately, the
sensor can be a flow meter located within surface production tubing
to determine no or little flow.
In another example embodiment, the sensor can be a vibration sensor
attached to a tubing string to measure an acceleration of the fluid
within the tubing string to determine a vibration signature
responsive to the measured acceleration of the fluid. The measured
vibration signature can then be compared to one or more
predetermined vibration signatures stored in memory and associated
with gas lock to thereby indicate gas lock.
Once the occurrence of gas lock is detected, embodiments of the
present invention can, for example, break the occurrence of gas
lock. The method can include, for example, maintaining a pump
operating speed. Maintaining a pump operating speed allows the well
fluid to remain above the pump in a static condition and allows the
gas bubbles in the fluid to rise above the fluid, facilitating a
separation of gas and liquid above the pump. After a waiting period
of a predetermined duration, the pump operating speed is reduced to
a predetermined value defining a flush value, thereby allowing the
well fluid to fall back through the pump, flushing out the trapped
gas. After a predetermined flush period, the pump operating speed
is restored to the previously maintained speed. The embodiments of
the present invention have the ability to flush the pump and return
the system back to production without requiring system shutdown. In
a preferred embodiment, the waiting period is between about 6 to 7
minutes, the flush period is between about 10 and 15 seconds, and
the pump operating speed is reduced during the flush period to
between about 20 and 25 Hz.
In addition, embodiments of the present invention provide for an
algorithm for optimizing an operating speed of the electrical
submersible pump assembly to maximize production without need for
operator intervention. The algorithm increases the pump operating
speed by a predetermined increment, e.g., 0.1 Hz, up to a preset
maximum pump operating speed, e.g., 62 Hz, when the instantaneous
value is continually above the threshold value for a predetermined
stabilization period, e.g., 15 minutes. The algorithm decreases the
pump operating speed by a predetermined increment, e.g., 0.1 Hz, if
the instantaneous value is continually below the threshold value
for a predetermined initialization period, e.g., 2 minutes.
Embodiments of this invention have significant advantages. Example
embodiments provide the ability to reliably detect a gas lock,
without operator intervention, based upon surface data and/or
downhole data. Also, example embodiments have the ability to break
a gas lock once detected, without requiring the system to be shut
down, improving efficiency and reliability in the production of
subterranean wells.
BRIEF DESCRIPTION OF DRAWINGS
Some of the features and benefits of the present invention having
been stated, others will become apparent as the description
proceeds when taken in conjunction with the accompanying drawings,
in which:
FIG. 1 is a side perspective view of an ESP assembly constructed in
accordance with an embodiment of the present invention;
FIG. 2 is a schematic side view of an ESP assembly constructed in
accordance with an embodiment of the present invention;
FIG. 3 is a flow diagram of a method of detecting and breaking gas
lock according to an embodiment of the present invention;
FIG. 4 is a flow diagram of a method of detecting and breaking gas
lock according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of controller for detecting and
breaking gas lock according to an embodiment of the present
invention; and
FIG. 6 is a schematic diagram of a controller having computer
program product stored in memory thereof according to an embodiment
of the present invention.
While the invention will be described in connection with the
preferred embodiments, it will be understood that it is not
intended to limit the invention to that embodiment. On the
contrary, it is intended to cover all alternatives, modifications,
and equivalents, as may be included within the spirit and scope of
the invention as defined by the appended claims.
DETAILED DESCRIPTION OF INVENTION
The present invention will now be described more fully hereinafter
with reference to the accompanying drawings in which embodiments of
the invention are shown. This invention may, however, be embodied
in many different forms and should not be construed as limited to
the illustrated embodiments set forth herein; rather, these
embodiments are provided so that this disclosure will be thorough
and complete, and will fully convey the scope of the invention to
those skilled in the art. Like numbers refer to like elements
throughout.
Embodiments of the present invention can detect an occurrence of
gas lock in an electrical submersible pump assembly by monitoring
via a sensor an instantaneous value of a property of a fluid
associated with an electrical submersible pump assembly and
comparing the instantaneous value to a threshold value over a
predetermined duration by a controller. Properties of a fluid
include conditions, such as, pressure, a differential pressure,
temperature, free gas detector, electrical resistivity, and flow.
The sensor can be located downhole or at the surface. Likewise, the
controller can be located downhole or at the surface.
With reference now to FIG. 1, one type of electrical submersible
pump (ESP) assembly in a well production system 10 includes a
centrifugal pump 22, a motor 20, and a seal assembly 23 located
between the pump 22 and motor 20, located with a well bore 28. The
system 10 further includes a variable speed drive 16 and data
monitoring and control device 12, e.g., a controller, typically
located on the surface 38 and associated with the variable speed
drive 16. The system 10 often includes a step-up transformer 21,
located between the variable speed drive 16 and a power cable 18.
The power cable 18 provides power and optionally communications
between the variable speed drive 16 and the motor 20. The variable
speed drive 16 may operate as a power source for providing
electrical power for driving the motor 20. The cable 18 typically
extends thousands of feet and thereby introduces significant
electrical impedance between the variable speed drive 16 (or
step-up transformer 21) and the motor 20. By altering the output
voltage and frequency of the variable speed drive 16, the
controller 12 associated with the variable speed drive 16 controls
the voltage at motor 20 terminals. Typically, the cable 18 connects
to a motor lead extension (not shown) proximate to the pumping
system. The motor lead extension continues in the well bore 28
adjacent the pump assembly and terminates in what is commonly
referred to as a "pothead connection" at the motor 20. In one
embodiment, the motor terminal comprises the pothead
connection.
FIG. 2 illustrates an exemplary embodiment of a well production
system 10, including a data monitoring and control device 12, e.g.,
a controller. The system 10 includes a power source 14 comprising
an alternating current power source such as an electrical power
line (electrically coupled to a power utility plant) or a generator
electrically coupled to and providing three-phase power to a motor
controller 16, which is typically a variable speed drive unit.
Motor controller 16 can be any of the well known varieties, such as
pulse width modulated variable frequency drives or other known
controllers which are capable of varying the speed of production
system 10. Both power source 14 and motor controller 16 are located
at the surface level of the borehole and are electrically coupled
to an induction motor 20 via a three-phase power cable 18. An
optional transformer 21 can be electrically coupled between motor
controller 16 and induction motor 20 in order to step the voltage
up or down as required.
Further referring to the exemplary embodiments illustrated in FIGS.
1 and 2, the well production system 10 also includes downhole
artificial lift equipment for aiding production, which comprises
induction motor 20 and electrical submersible pump 22 ("ESP"),
which may be of the type disclosed in U.S. Pat. No. 5,845,709.
Motor 20 is electromechanically coupled to and drives pump 22,
which induces the flow of gases and liquid up the borehole to the
surface for further processing. Three-phase cable 18, motor 20,
motor controller 16, and pump 22 form an ESP system.
Pump 22 can be, for example, a multi-stage centrifugal pump having
a plurality of rotating impeller and diffuser stages which increase
the pressure level of the well fluids for pumping the fluids to the
surface location. The upper end of pump 22 is connected to the
lower end of a discharge line 34 for transporting well fluids to a
desired location. Typically, a seal section 23 is connected to the
lower end of pump 22, and a motor 20 is connected to the lower end
of the seal section for providing power to pump 22.
Well production system 10 also includes data monitoring and control
device 12, typically a surface unit, which may communicate with
downhole sensors 24a-24n via, for example, bi-directional link 24
or alternately via cable 18. In an exemplary embodiment, sensors
24a-24n monitor and measure various conditions within the borehole,
such as pump discharge pressure, pump intake pressure, tubing
surface pressure, vibration, ambient well bore fluid temperature,
motor voltage and/or current, motor oil temperature and the like.
Although not shown, data monitoring and control device 12 may also
include a data acquisition, logging (recording) and control system
which would allow device 12 to control the downhole system based
upon the downhole measurements received from sensors 24a-24n via,
for example, bi-directional link 24. Sensors 24a-24n can be located
downhole within or proximate to induction motor 20, ESP 22 or any
other location within the borehole. Any number of sensors may be
utilized as desired.
Further referring to FIG. 2, data monitoring and control device 12
is linked to sensors 24a-24n via communication link 24 and motor
controller 16 via link 17 in order to detect and break gas locks
without requiring system shutdown. In an example embodiment, the
gas lock detecting and breaking functionality of device 12 is
conducted based solely upon surface data, such as current, voltage
output and/or torque, received from motor controller 16 via
bi-directional link 17. In other embodiments, the functionality may
also be affected based upon data received from one or more of
downhole sensors 24a-24n.
Data monitoring and control device 12 communicates over well
production system 10, using the communication links described
herein, on at least a periodic basis utilizing techniques, such as,
for example, those disclosed in U.S. Pat. No. 6,587,037, entitled
METHOD FOR MULTI-PHASE DATA COMMUNICATIONS AND CONTROL OVER AN ESP
POWER CABLE and U.S. Pat. No. 6,798,338, entitled RF COMMUNICATION
WITH DOWNHOLE EQUIPMENT. Device 12 is coupled to motor controller
16 via bi-directional link 17 in order to receive measurements such
as, for example, amperage, current, voltage and/or frequency
regarding the three phase power being transmitted downhole. Such
control signals would regulate the operation of the motor and/or
pump 22 to optimize production of the well production assembly 10,
such as, for example, detecting and breaking gas locks. Moreover,
these control signals may be transmitted to some other desired
destination for further analysis and/or processing.
Data monitoring and control device 12 controls motor controller 16
by controlling such parameters as on/off, frequency (F), and/or
voltages, each at one of a plurality of specific frequencies, which
effectively varies the operating speed of motor 20. Such control is
conducted via link 17. The functions of device 12 may execute
within the same hardware as the other components comprising device
12, or each component may operate in a separate hardware element.
For example, the data processing, data acquisition/logging and data
control functions of the present invention can be achieved via
separate components or all combined within the same component.
During production, some wells produce gas along with oil. As such,
there is a tendency for the gas to enter the pump assembly 22 along
with the well fluid, which can decrease the volume of oil produced
or may even lead to a "gas lock." A gas lock is a condition in an
ESP assembly in which gas interferes with the proper operation of
impellers and other pump components, preventing the pumping of
liquid.
Referring to FIG. 3, an exemplary algorithm for detecting and
breaking a gas lock will now be described. Data monitoring and
control device 12 also comprises a processor and memory which
performs the logic, computational, and decision-making functions of
the present invention and can take any form as understood by those
in the art. See, e.g., FIGS. 5 and 6. The memory can include
volatile and nonvolatile memory known to those skilled in the art
including, for example, RAM, ROM, and magnetic or optical disks,
just to name a few.
At step 201, data monitoring and control device 12, e.g., the
controller, continuously monitors the output current, voltage
and/or torque of motor controller 16 via bi-directional link 17 in
order to detect and break gas locks in accordance with the present
invention. However, in the alternative, output measurements from
downhole sensors 24a-24n may also be monitored. At step 203, data
monitoring and control device 12 will generate a threshold value of
the motor current and/or torque from historical data. The threshold
value can be based on a historical value, such as a long-term
average of the motor current or motor torque using a time constant
long enough to filter out any short term variations in such
measurements. Alternately, the threshold value can be based on
another historical value, such as a peak value for given data
window. When a gas lock does occur, the motor current or motor
torque will typically decrease by 30-50%. To determine a 30% drop
in the motor torque and/or current, the threshold value can be
generated to be, for example, 70% of a long-term average value.
Alternately, the threshold value can be generated to be 65% to 75%
of a peak value for a given historical data window, i.e., a
predetermined period of between 2 and 5 minutes, preferably the
last 3 minutes. Thereafter, at step 205, the instantaneous value is
continuously compared to the threshold value. In another preferred
embodiment, the motor torque is measured instead of the motor
current because the torque is more sensitive to downhole phenomena.
If control device 12 does not detect an occurrence of gas lock
based on the comparison in step 207, the algorithm loops back to
step 201 and begins the process again.
Should data monitoring and control device 12 detect an occurrence
of gas lock, control device 12 will proceed to step 209. At this
step, control device 12 will instruct motor controller 16 via link
17 to maintain the same operating speed for a predetermined waiting
period. In the most preferred embodiment, this waiting period has a
length of 6 to 7 minutes, however, other waiting periods, including
a waiting period of 3 to 15 minutes, can be programmed based upon
design constraints. In an alternative embodiment, the waiting
period will be limited, at least in part, by a predetermined
maximum pump temperature, which would be communicated to device 12
from downhole sensors 24a-24n via communication link 24.
Further referring to the exemplary algorithm of FIG. 3, as motor 20
maintains this operating speed at step 209, it produces a somewhat
static condition as pump 22 produces just enough head to support
the column of fluid in the tubing above, but not enough to pump the
fluid upwards to the surface. As a result, the gas bubbles in the
fluid directly over the pump begin to rise, while the fluid settles
and becomes denser.
At step 211, data monitoring and control device 12 ends the waiting
period and decreases the operating frequency to a lower value, such
as, for example, 20-25 Hz. The normal operating frequency is
typically set at 60 Hz, This decreased operating frequency is
maintained for a predetermined period of time, such as, for
example, 10-15 seconds. During this time, pump 22 can no longer
support the fluid column just above it and, thus, the fluid begins
to fall back through pump 22, flushing out the trapped gas. At the
end of this low speed period of step 211, device 12 increases the
operating frequency of pump 22 back to normal and production begins
again at step 213.
Embodiments of the present invention further provide an algorithm
for optimizing an operating speed of the electrical submersible
pump assembly to maximize production without need for operator
intervention. The algorithm increases the pump operating speed by a
predetermined increment, e.g., between 0.08 and 0.4 Hz, preferably
0.1 Hz, up to a preset maximum pump operating speed, e.g., 62 Hz,
when the instantaneous value is continually above the threshold
value for a predetermined stabilization period, e.g., between 10 to
20 minutes, preferably 15 minutes. The algorithm decreases the pump
operating speed by a predetermined increment, e.g., between 0.08
and 0.4 Hz, preferably 0.1 Hz, if the instantaneous value is
continually below the threshold value for a predetermined
initialization period, e.g., between 90 seconds and 3 minutes,
preferably 2 minutes. In the absence of gas lock or gas bubbles for
a reasonable period of time, the algorithm increases the pump
operating speed in a step-wise fashion to maximize production. In
the presence of gas bubbles but not true gas lock, the algorithm
does not alter the pump operating speed. Gas bubbles, without
causing an occurrence of gas lock, can cause a temporary drop in
the motor current or motor torque as understood by those skilled in
the art. If the algorithm detects an occurrence of gas lock, in
which the instantaneous value is continually below the threshold
value for a period of time, e.g., 2 minutes, the algorithm lowers
the pump operating speed (and the rate of production) by a small
increment to better adjust to the level of gas and attempt to
prevent further occurrences of gas lock as understood by those
skilled in the art.
As illustrated in FIG. 4, embodiments of the present invention can
include a method 150 of detecting a gas lock in an electrical
submersible pump assembly. The method 150 can include monitoring
via a sensor 24a-24n an instantaneous value of a property of a
fluid associated with an electrical submersible pump assembly (step
152). The assembly can include a multi-stage electrical submersible
pump 22 having an inlet 35 and a discharge 36, a pump motor 20 to
drive the pump 22, a discharge line 34 for transporting pumped
fluid from the pump discharge to the surface 38, and a controller
12 configured to receive data from the sensor 24a-24n and to detect
an occurrence of gas lock in the electrical submersible pump
assembly. The method 150 can also include comparing the
instantaneous value to a threshold value over a predetermined
duration by the controller 12 to thereby detect the occurrence of
gas lock in the electrical submersible pump assembly (step 153). If
gas lock is detected by the controller (step 154), the method can
further include breaking the detected occurrence of gas lock by:
maintaining a pump operating speed for a first predetermined
duration defining a waiting period to facilitate a separation of
gas and liquid located above the pump (step 155), reducing the pump
operating speed to a predetermined value defining a flush value for
a second predetermined duration defining a flush period so that the
fluid located above the pump falls back through the pump flushing
out any trapped gas (step 156), and restoring the pump operating
speed to the previously maintained pump operating speed (step 157).
In a preferred embodiment, the waiting period is between 6 to 7
minutes, the flush period is between 10 and 15 seconds, and the
pump operating speed is reduced during the flush period to between
20 and 25 Hz.
In an example embodiment, the sensor 24a-24n can be a differential
pressure gauge for measuring a differential pressure of the fluid
in the pump between the pump inlet 35 and pump discharge 36, e.g.,
the bottom and top of the pump, to determine a drop in pressure.
For example, a decrease of about 50% of a normal pressure, e.g., an
average pressure, for a period of about 30 seconds can indicate gas
lock.
In another example embodiment, the sensor 24a-24n can be a pressure
gage located in a pump stage located toward the inlet 35, e.g., the
bottom stages of the pump, to determine a drop in pressure. For
example, a decrease of about 30% of a historical pressure, e.g., a
peak pressure of the past three (3) minutes, for a period of about
30 seconds can indicate gas lock.
In yet another example embodiment, the sensor 24a-24n can be a
fluid temperature sensor located toward the discharge 36, e.g., the
top of the pump, to determine an increase in temperature. For
example, an increase of about 20% of a historical temperature,
e.g., a rolling average of the values over the past five (5)
minutes, for a period of about 30 seconds can indicate gas
lock.
In another example embodiment, the sensor 24a-24n can be a free gas
detector located within the pump to determine a high level of free
gas of a function of volume. For example, a level of free gas above
about 50% by volume for a period of about 30 seconds can indicate
gas lock.
In another example embodiment, the sensor 24a-24n can be an
electrical resistivity gage located within the pump to determine a
high level of resistivity. For example, a high level of resistivity
of about 200 Ohms per cm or more for a period of about 30 seconds
can indicate gas lock.
In another example embodiment, the sensor 24a-24n can be a flow
meter located within surface production tubing to determine no or
little flow. For example, a flow of about zero for a period of
about 30 seconds can indicate gas lock.
In another example embodiment, the sensor 24a-24n can be a
vibration sensor attached to a tubing string to measure an
acceleration of the fluid within the tubing string to determine a
vibration signature, or characteristic pattern of vibration,
responsive to the measured acceleration of the fluid. The vibration
signature can refer to the actual signal from a vibration sensor
and also the spectrum, or frequency-based representation. The
determined vibration signature can then be compared to one or more
predetermined vibration signatures stored in memory and associated
with gas lock to thereby indicate gas lock. The predetermined
vibration signatures can be determined by testing as understood by
those skilled in the art. As understood by those skilled in the
art, a vibration sensor can include an XY vibration sensor, which
is a sensor that measures vibration or acceleration in two
dimensions, or along two axes. As described in jointly-owned
pending U.S. patent application Ser. No. 12/360,677, titled
"Electrical Submersible Pump Rotation Sensing Using an XY Vibration
Sensor," filed on Jan. 27, 2009, which is incorporated herein in
its entirety, the measurements for the two dimensions can be
correlated through a Fourier analysis, or other frequency analysis
as understood by those skilled in the art, to determine a frequency
and direction of rotation of an ESP.
Example embodiments can include different durations for determining
gas lock. As understood by those skilled in the art, too short of a
duration can result in false positives; similarly, too long of a
duration can result in delayed detection, perhaps resulting in
damage to the motor. Example embodiments can include a
predetermined duration for the comparison a period between about 15
seconds and about 1 minute.
Embodiments of the present invention have significant advantages.
Example embodiments have the ability to reliably detect a gas lock,
without operator intervention, based upon surface data and/or
downhole data. Also, example embodiments have the ability to break
a gas lock once detected, without requiring system to be shut
down.
Embodiments of a data monitoring and control device 12, e.g., a
controller, may take various forms. In one embodiment, the control
device 12 may be part of the hardware located at the well site,
included in the software of a programmable ESP controller, variable
speed drive, or may be a separate box with its own CPU and memory
coupled to such components. Also, control device 12 may even be
located across a network and include software code running in a
server which bi-directionally communicates with production system
10 to receive surface and/or downhole readings and transmit control
signals accordingly.
As illustrated in FIG. 5, example embodiments include a controller
12, having, for example, input-output I/O devices, e.g., an
input/output interface 61; one or more processors 62; memory 63,
such as, tangible computer readable media; and optionally a display
65. The memory 63 of the controller can include program product 64
as described herein.
As illustrated in FIGS. 5 and 6, embodiments of the present
invention include a memory 63 having stored therein a program
product, stored on a tangible computer memory media, operable on
the processor 62, the program product comprising a set of
instructions 70 that, when executed by the processor 62, cause the
processor 62 to detect an occurrence of gas lock by performing
various operations. The operations include: monitoring an
instantaneous value utilizing the sensor 71 and comparing the
instantaneous value to a threshold value over a predetermined
duration to thereby detect the occurrence of gas lock in the
electrical submersible pump assembly 72. The operations further
include breaking the detected occurrence of gas lock by the
substeps of: (a) maintaining a pump operating speed for a first
predetermined period defining a waiting period to facilitate a
separation of gas and liquid located above the pump, (b) reducing
the pump operating speed to a predetermined value defining a flush
value for a second predetermined period defining a flush period so
that the fluid located above the pump falls back through the pump
flushing out any trapped gas, and (c) restoring the pump operating
speed to the previously maintained pump operating speed 73.
Example embodiments also include computer program product stored on
a tangible computer readable medium that is readable by a computer,
the computer program product comprising a set of instructions that,
when executed by a computer, causes the computer to perform the
various operations. The operations can include detecting an
occurrence of gas lock in a electrical submersible pump assembly,
including (i) monitoring an instantaneous value associated with the
pump motor of the electrical submersible pump assembly, (ii)
generating a threshold value based on historical data of values
associated with the pump motor of the electrical submersible pump
assembly, and (iii) comparing the instantaneous value to the
threshold value to thereby detect the occurrence of gas lock in the
electrical submersible pump assembly. The operations can further
include breaking the detected occurrence of gas lock, including (i)
maintaining a pump operating speed for a first predetermined
duration defining a waiting period to facilitate a separation of
gas and liquid located above the pump, (ii) reducing the pump
operating speed to a predetermined value defining a flush value for
a second predetermined duration defining a flush period so that the
fluid located above the pump falls back through the pump flushing
out any trapped gas, and (iii) restoring the pump operating speed
to the previously maintained pump operating speed.
It is important to note that while embodiments of the present
invention have been described in the context of a fully functional
system and method embodying the invention, those skilled in the art
will appreciate that the mechanism of the present invention and/or
aspects thereof are capable of being distributed in the form of a
computer readable medium of instructions in a variety of forms for
execution on a processor, processors, or the like, and that the
present invention applies equally regardless of the particular type
of signal bearing media used to actually carry out the
distribution. Examples of computer readable media include but are
not limited to: nonvolatile, hard-coded type media such as read
only memories (ROMs), CD-ROMs, and DVD-ROMs, or erasable,
electrically programmable read only memories (EEPROMs), recordable
type media such as floppy disks, hard disk drives, CD-R/RWs,
DVD-RAMs, DVD-R/RWs, DVD+R/RWs, flash drives, and other newer types
of memories, and transmission type media such as digital and analog
communication links. For example, such media can include both
operating instructions and/or instructions related to the system
and the method steps described above.
Moreover, it is to be understood that the invention is not limited
to the exact details of construction, operation, exact materials,
or embodiments shown and described, as modifications and
equivalents will be apparent to one skilled in the art. For
example, although the present invention has focused on measurements
of motor torque and/or current, other measurements could also be
used to indicate a gas locked state. In the drawings and
specification, there have been disclosed illustrative embodiments
of the invention and, although specific terms are employed, they
are used in a generic and descriptive sense only and not for the
purpose of limitation. Accordingly, the invention is therefore to
be limited only by the scope of the appended claims.
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